FIG. 1 shows a layout diagram of a display panel and a power supply system for supplying the display panel with a power supply voltage. The display panel as shown in FIG. 1 may include a plurality of display panel elements. These display panel elements may include liquid crystal display elements or for example organic light emitting diode (OLED) elements. An organic light emitting diode is a light emitting diode (LED) in which an emissive electroluminescent layer is formed by a film of organic compounds which can emit light in response to an electric current. This layer of organic material is located between two electrodes wherein at least one of these electrodes is transparent. A display panel having OLED elements can operate without a back light. As shown in FIG. 1, the power supply circuit supplies the display panel elements within the display panel with a power supply voltage.
FIG. 2 is a circuit diagram of the display panel and the power supply system shown in FIG. 1. The display panel in FIG. 2 includes a display panel element DPE. The display panel element DPE as shown in FIG. 2 within the display panel has an organic light emitting diode OLED which is supplied with a positive power supply voltage PVDD and a negative power supply voltage PVEE wherein the positive power supply voltage PVDD may typically range from +5 Volts to +6 Volts and the negative power supply voltage PVEE may be in a range from −5 Volts to −6 Volts. The display panel element that includes an OLED is driven by a display driver DD. The display driver DD receives a voltage PVDD as the positive supply voltage of the display panel element, and a voltage VSS (Ground voltage which normally has a potential of zero Volts) as the negative supply voltage. The supply voltage of the display panel elements within the display panel is provided by an external power supply regulator PSR which forms an external component and is controlled by a switching control circuit SWREG which may be integrated into an integrated power supply circuit chip. The integrated switching control circuit SWREG controls the power supply regulator PSR by applying control signals to transistors of the power supply regulator PSR as shown in FIG. 2. As can be seen in FIG. 2, the power supply regulator PSR includes two symmetrical power supply units PSUA, PSUB for regulating the positive power supply voltage PVDD and the negative power supply voltage PVEE of the display panel element DPE within the display panel. The negative power supply unit PSUA includes a transistor TA, a coil LA, a diode DA and a capacitor CA. The positive power supply unit PSUB includes a transistor TB, a coil LB, a diode DB and a capacitor CB. The transistors TA and TB of the power supply regulator PSR are controlled by switching control signals CRTLA and CRTLB output by the switching control circuit SWREG of the power supply circuit chip. The display panel element DPE as shown in FIG. 2 includes a selection transistor TSEL which is controlled by a selection signal CRTL-SEL to activate the display panel element. The selection transistor TSEL is switched in response to the switching control signals CRTLA and CRTLB when a driving voltage is applied to the gate of a switching transistor TSW of the display panel element which applies the positive power supply voltage PVDD to the organic light emitting diode OLED as shown in FIG. 2. The display panel element further includes a capacitance CDPE which may have a parasitic capacitance. The power supply regulator PSR regulates the positive power supply voltage PVDD and the negative power supply voltage PVEE of the display panel element DPE in response to the control signals CRTLA, CRTLB received from the switching control circuit SWREG. The power supply regulator PSR is connected to a battery as shown in FIGS. 1 and 2.